1. Field of the Invention
This invention relates to a method of providing a water impervious membrane covering for a roof by coating a cloth with silicone elastomeric compositions.
2. Description of the Prior Art
Many systems have been devised for providing a roof covering for buildings. One method uses pieces of water-impervious material, such as slate or wood, layed upon the roof in overlapping rows so that each joint is covered by the piece layed above it. Such shingled roofs are satisfactory when the roof is pitched at a high angle so that there is no tendency for the water to flow back through the cracks between the pieces. Even in these cases, when located in areas where freezing occurs, ice occasionally forms on the lower edges of roofs to form a dam which forces water back through the cracks into the interior of the building.
A method of covering roofs that did not have cracks in them was evolved making use of asphalt as an impregnant and bonding agent along with felts of various fibers. The asphalt in the form of a hot liquid or an emulsion was spread over the roof, then pieces of asphalt impregnated felt were rolled out over it. Another layer was then applied, moving the location of the seams so that they did not occur in the same area. Such built up roofs eliminated the problem of water backing up from ice dams. Built up roofs could also be used when the roof was of a low pitch or flat as there were no cracks for water to back up through. The built up roofs fail due to cracks developing because of exposure to weathering and embrittlement of the felt, oxidation of the asphalt, and expansion and contraction of the system because of temperature changes. During cold weather, the asphalt becomes brittle and easily cracks due to expansion and contraction forces.
Systems have been developed based upon sheets of rubber or plastic intended to correct the problem of failure due to weathering and cracking from temperature changes. The sheets used have some elasticity so that they can move as the underlying structure expands and contracts over the course of the changing seasons. However, there are still problems remaining. Many of the coatings are satisfactory at normal temperatures, but become overly soft at high temperatures or overly hard at very low temperatures.
Because these are also the times that building movements are at a maximum, failures result. The plastic materials tend to lose volatile components and become brittle with age. The rubber-based materials are not always compatible with the underlying roof structure and special steps must be taken to make sure they do not contact asphaltic materials.
A system has been devised which coats the roof structure with a polyurethane foam which insulates the underlying structure. The polyurethane foam cannot withstand the effects of sunlight, so it is covered with an opaque layer of silicone rubber based paint to provide weatherability to the system. The system requires special equipment and skilled operators for installation.
Repairs on roofs have been made by coating a roof surface with a solvent or emulsion based asphalt, rolling down an impregnated glass fiber mat and overcoating with more of the asphalt. Another system involves the simultaneous spraying of asphalt solvent dispersions or aqueous emulsions with chopped glass reinforcement over a saturated felt to give a reinforced membrane. This system is said to provide a simpler roofing system with comparable life to a conventional asphalt and felt built up roof. Experience has shown that systems based on asphalt do not have a satisfactory life without regular maintenance.